In general, most furniture such as desks, cabinets, or industrial computer cabinets, etc., are provided with slide rail devices, so that a movable member can be combined with a fixing member by using the slide rail devices. In order to improve the smoothness of the movable member during sliding, a three-section type slide rail device is developed, which includes an outer slide rail, a middle slide rail and an inner slide rail. The outer slide rail is fixedly mounted on the fixing member, such as a cabinet, and the inner slide rail is fixedly mounted on a side wall of the movable member, such as a server. In this case, the inner slide rail and the middle slide rail can be push or pulled reciprocally relative to the outer slide rail along the longitudinal direction of the three-section slide rail device. Therefore, the movable member can be pulled out or retracted relative to the fixing member.
In order to properly conduct the sliding operation of a conventional slide rail device, a locking mechanism is usually provided between the outer slide rail and the middle slide rail. When the slide rail device is pulled out, the middle slide rail can be fixed at an uttermost position by the locking mechanism. When the inner slide rail is retracted, the fixed state of the middle slide rail is released and can be pulled back synchronously. However, when the inner slide rail and the movable member, such as the server, are removed from the slide rail device, the middle slide rail that has been fixed in an extended state cannot be unlocked using the inner slide rail. At this time, the middle slide rail is exposed and protruded, which occupies outside space and may obstruct the closing of a door.